A variety of erasable ink composition to write on an impervious writing surface to provide writing thereon which is readily erasable by wiping with, for example, an eraser made of felt are already known, as disclosed in, for example, Japanese Patent Application Laid-open No. 63-43981, No. 62-265377 and No. 2-129278. However, these prior erasable ink compositions contain carboxylic acid esters, liquid paraffin, silicone resins or nonionic surfactants as a separating agent therein, and thus it is known that they provide writing which is insufficiently erasable depending upon the material of impervious writing surface. Namely, the prior erasable ink compositions have erasability dependendent on the material of impervious writing surface. It is also known that such an ink composition provides writing which is not readily erasable after long standing. Namely, the prior erasable ink compositions have erasability dependendent on time.